The subject invention relates to signal processing, particularly for identifying and analyzing information that changes against an unchanging or slowly changing background. The invention is particularly useful in processing image information from an array of infrared detectors.
Conventional target detection using infrared (IR) passive sensors is based upon conversion IR energy into electrical signals. Due to noise from various signal sources, such as the optics, detectors, and the electronic circuits, the raw signal to noise ratio (SNR) s typically so low that it is necessary to improve the SNR by integrating the detector output signals during a certain period of time. This process is "called integrate and dump" and usually is combined with the pre-amplification of the detector output signals. The circuitry to perform these functions increases the complexity of the focal plane electronics, and increases the power requirements for the device.
Since a typical passive sensor consists of a 512.times.512 or 1024 .times.1024 array of detectors, the signals from the detector array are multiplexed in the time domain so that they can be read out using a reduced number of output channels from the detector array to the other signal processing circuitry. The time division multiplexed signals are then digitized through an analog to digital converter (ADC). The two processing functions, time division multiplexing, and analog to digital conversion, require a very high sampling rate, and cause aliasing for wide-band signals, which results in signal distortion.
In practical operation of a focal plane array, the infrared energy received on the focal plane represents images that are cluttered by heavy background information. The type of background information depends upon the orientation of the focal plane relative to the desired observation, such as an earth background, space background, and so forth. Therefore, target detection in the background has been considered for some time as a very challenging process. This target detection consists of two parts. The first is to remove the background clutter from the target, and the other is to detect target motion. The conventional technique to remove the background clutter is frame to frame subtraction of the image on the focal plane. Target motion detection can only be accomplished by complex state estimation algorithms and/or correlation on the frame to frame data. Computations of these algorithms is complex, time consuming, and consequently requires a very high throughput processors and considerable electrical power.
Thus, the conventional processing technique for IR detector signals requires multistage signal processing for the pre-amplification, time division multiplexing, analog to digital conversion, background removal, and target motion detection functions.